CNC Precision Machining, Everything You Need To Know

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CNC Precision Machining, Everything You Need To Know

CNC precision machining is a process that is used in the manufacturing industry. It is a computer-controlled process that uses geometric data to control the machine tools.

The CNC precision machining process has many benefits for the manufacturing industry. It helps companies save time, reduce costs, and ensure accuracy.

This article will discuss what CNC precision machining is, how it works and why it’s important for the manufacturing industry.

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What is CNC Precision Machining?

When you wondering “What is CNC precision machining?”, here is the answer: CNC precision machining technology is a subtractive manufacturing process that automates the machine tools with help of Computer Aided Design (CAD) and Computer Aided Machining(CAM) to carry out various operations for cutting/drilling metal or plastic workpiece from solid block material final desired shape of parts which has high accuracy & precision (usually refers to the accuracy of 10 ~ 0.1μm surface roughness is Ra0.16—0.01μm).

01. Accuracy: Refers to the degree of closeness between the obtained measurement results and the true value. The high accuracy of measurement means that the systematic error is small. At this time, the average value of the measured data deviates less from the true value, but the data is scattered, that is, the size of the accidental error is not clear.

02. Precision: Refers to the reproducibility and consistency between the results obtained by repeated measurements using the same spare sample. It is possible to have high precision, but the precision is not exact. For example, the three results obtained by using the length of 1mm to measure are 1.051mm, 1.053, and 1.052 respectively. Although they have high precision, they are not accurate.

Accuracy means the correctness of the measurement results, precision means the repeatability and reproducibility of the measurement results, precision is the prerequisite for accuracy.

What is CNC Precision Machining?

In the past, the process of making a custom part would require a lot of time and effort on behalf of the customer. For example, if a customer wanted to make a custom part for an engine, it might take weeks or even months for them to receive their order. This is because they first need to design the part, then send it off to be made before finally receiving it back.

However, this process can now be done in much less time thanks to CAD/CAM and 3D printing technology. These technology allows customers to create their own custom parts by uploading their designs in CAD and specifying how they want them made. They can even make changes and updates on the fly with this tool!  The processes of CNC precision machining to make a custom part involve the following steps:

  1. – Designing the part using CAD software
  2. – Creating a toolpath using CAM software
  3. – Generating G code to control the machine tools
  4. – Programming the machine tools and loading them with materials
  5. – Machining the part using CNC machines (cnc mill, cnc lathe, cnc router etc.) with follow machining processes:

Cutting: This is the process of removing excess material from a part by using a tool to remove material in a controlled manner.                        Shaping: This is the process of changing the shape of a part by cutting away excess material from it.                                                          Finishing: This is the process of creating an even surface finish on a part that has been cut or shaped with an end mill or other tool.

Tolerance of Precision Machining

We deal with machining processes every day, and we often talk about precision, but is the precision you said right? 

Machining accuracy is the level which the actual size, shape, position of the machined part surface conforms to the ideal geometric parameters required by the drawing! The ideal geometric parameters, in terms of size, are the average size; in terms of shape, they are absolute circles, cylinders, planes, cones, and straight lines; for mutual positions, they are absolute parallel, perpendicular, coaxial, Symmetry etc.

1. Dimensional accuracy: The degree of conformity between the actual size of the processed part and the center of the tolerance zone of the part size.

2. Shape accuracy: Refers to the degree of conformity between the actual geometric shape of the processed part surface and the ideal geometric shape.

3. Position accuracy: Refers to the difference in actual position accuracy between the relevant surfaces of the machined parts.

4. Mutual relationship: Usually, when designing machine parts and specifying the machining accuracy of parts, attention should be paid to controlling the shape error within the position tolerance, and the position error should be smaller than the size tolerance. That is, for precision parts or important surfaces of parts, the shape accuracy requirements should be higher than the position accuracy requirements, and the position accuracy requirements should be higher than the dimensional accuracy requirements. The deviation between the actual geometric parameters of the part and the ideal geometric parameters is called the machining error. The size of the machining error reflects the level of machining accuracy. The larger the error, the lower the machining accuracy, and the smaller the error, the higher the machining accuracy.

Tolerance of Precision Machining

Introduction of tolerance for precision machining:


Although the tools of cnc machines are high precision, these machines cannot accurately reproduce the dimensions of products just as they are in the 3D drawings. Therefore, engineers set up tolerances for all dimensions on the CAD drawing for manufacturing the parts.

Tolerance is the amount of deviation in the dimension of a part that is acceptable by conventional standards. A synonym for it is dimensional accuracy. There is no standard tolerance for all precision CNC machining processes. The strictness of tolerance depends on the manufacturing process. The number of decimal places a tolerance value has shows the strictness of the measurement.

Machining accuracy is mainly used for mechanical parts, and accuracy is a term used to evaluate the geometric parameters of the machined surface. Machining accuracy is measured by tolerance grade, the smaller the grade value, the higher the precision.

The actual size obtained by any processing method will not be absolutely accurate. As long as the precision is within the tolerance range required by the part drawing, the processing technology and equipment with the lowest machining cost should be selected.

Linear dimension precision grade (mm)
Tolerance Grades0~3>3~6>6~30>30~120>120~400>400~1000>1000~2000>2000
Rounding radius and chamfer height dimension precision grade (mm)
Tolerance Grades0~33~6>6~30>30

More information you need, please reach us at 

Author: Mose Li

Author: Mose Li

Director of Project Engineering at 3Q Machining

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